As methods for evaluation of resolution in charged particle microscopes (such as a Scanning Electron Microscope (SEM) and a scanning ion microscope), the followings have been known. A first method is a GAP method according to which a sample having gold particles vapor-deposited on carbon is observed with a microscope and a minimal gap distance between two points which can be confirmed with eyes on an observed image is used for evaluation as disclosed in Patent Literature 1. A second method is an FFT method in which, the frequency analysis by two-dimensional Fourier transform of data of an observed image is conducted and the image resolution is evaluated as described in Patent Literature 2. A third method is to evaluate the image resolution from a local contrast gradient in observed image data as disclosed in Patent Literature 3.
On the other hand, in a charged particle beam device represented by a scanning electron microscope, desired information (for example, a sample image) is obtained from a sample by scanning a finely focused charged particle beam on the sample. In such a charged particle beam device, when the optical axis misaligns to a lens, a lens aberration occurs to decrease the resolution of the sample image and, therefore, highly accurate axis adjustment is necessary for obtaining a sample image of high resolution. In the axis adjustment, the excitation current or the like of an objective lens is changed periodically and the operating conditions of a deflector for axis adjustment (aligner) is manually adjusted so as to minimize the movement at that time.
As a technique for conducting the above adjustment automatically, a technique disclosed in Patent Literature 4 is available. The description discloses a technique of changing the excitation set value of an alignment coil based on a shift of the electron beam irradiation position which changes between two excitation conditions of an objective lens. Further, Patent Literature 5 discloses a technique for performing focus correction based on a detected positional shift between two images of an electron microscope obtained under different optical conditions.
Furthermore, when an axially asymmetric aberration exists in the charged particle beam device, the focal point differs in longitudinal and lateral directions of an image and the image is blurred in a certain direction. This can be adjusted with a stigmator and the adjustment can be conducted automatically like the automatic axis adjustment. An ordinary user confirms with eyes that the image quality after automatic adjustment is satisfactory. If unsatisfactory, the adjustment will be executed again.